The RDF module introduces RDF and RDFa to Drupal. RDF is a W3C standard to
describe structured data. RDF can be serialized as RDFa in XHTML attributes
to augment visual data with machine-readable hints.

Modules can provide mappings of their bundles' data and metadata to RDF
classes and properties. This module takes care of injecting these mappings
into variables available to theme functions and templates. All Drupal core
themes are coded to be RDFa compatible.